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Title: First Report of Southern Blight on Bottle Gourd (Lagenaria siceraria) caused by Sclerotium Rolfsii in South Carolina

Author
item Ling, Kai-Shu
item Kousik, Chandrasekar - Shaker
item KEINATH, ANTHONY - CLEMSON UNIVERSITY

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2008
Publication Date: 4/1/2008
Citation: Ling, K., Kousik, C.S., Keinath, A.P. 2008. First Report of Southern Blight on Bottle Gourd (Lagenaria siceraria) caused by Sclerotium Rolfsii in South Carolina. Plant Disease. 92:656.

Interpretive Summary: Bottle gourd [Lagenaria siceraria (Mol.) Standl.] is an important rootstock for watermelon grafting. We are currently testing bottle gourds for disease resistance. In the summer of 2007, symptoms of wilting and crown necrosis were observed in bottle gourd plants in a field in Charleston, South Carolina. Thirty five of eighty-five plants examined (41%) had stem rot at the crown area just above the soil line. Identification of the isolated fungus as Sclerotium rolfsii was based on fungal colony morphology and the high nucleotide sequence identity (99%) in the internal transcribed space (ITS) region to other S. rolfsii and Athelia rolfsii (perfect stage of S. rolfsii). Although Southern blight caused by S. rolfsii has been reported on many crop plants in the southern United States, this disease has not been reported previously on bottle gourd in North America. Identifying sources of resistance to Southern blight in bottle gourds may be necessary to make them suitable as rootstocks in areas where S. rolfsii is present.

Technical Abstract: Bottle gourd (Lagenaria siceraria [Mol.] Standl.) is an important rootstock in watermelon grafting in Asia and Middle East and is gaining momentum in the United States. We are currently testing bottle gourds for disease resistance. In the summer of 2007, symptoms of wilting and crown necrosis were observed in bottle gourd seedlings one month after transplanting in a field in Charleston, South Carolina. In October, 2007, 35 of 85 plants examined (41%) had stem rot at the crown area just above the soil line where coarse white mycelia with abundant sclerotia were observed. Sclerotium rolfsii was isolated from all four wilted plants. PCR product of approximately 680 bp was amplified from DNA extracted from two isolates using the primers ITS1 and ITS4 and sequenced. BLASTn analysis of the sequence in the NCBI databases (http://www.ncbi.nlm.nih.gov/) revealed 99% similarity to the internal transcribed space (ITS) sequences of Sclerotium rolfsii and Athelia rolfsii (perfect stage of S. rolfsii). Pathogenicity of the two isolates was tested on young seedlings and adult (10-wk-old) bottle gourd plants. S. rolfsii was re-isolated from the inoculated plants on medium. Although Southern blight caused by S. rolfsii has been reported on many crop plants in the southern United States, this disease has not been reported previously on bottle gourd in North America. Identifying sources of resistance to Southern blight in bottle gourds may be necessary to make them suitable as rootstocks in areas where S. rolfsii is present.